93 chev 5.7 LOW engine temp

My friend has a 93 Chev conversion van with 5.7... poor heater output. He
has an aftermarket temp guage that shows engine runs about 125 degrees F.
He also told me the Dealership replaced the thermostat and it didn't seem to

help.
I attached my Snap on MT2500 and confirmed that ECM sees about the same
temperature as his guage does. We headed down the road (it was about 35 to
40 degrees F that day) and I watched engine temp fall to about 110 F.
Then he shows me this receipt from the dealership which I will quote below:
CUSTOMER STATES HE NEEDS A NEW THERMASTAT (yeah, that's how they spelled
that)
VAN HAS POOR HEAT LAST FEW DAYS. DOES NOT SEE ANY LEAKS ON
GROUND AND HAS NOT ADDED ANY COOLANT
NOTE: HAS AFTERMARKET TEMP GUAGE, BOTTOM LEFT OF DASH
IS ACCURATE
VERIFY CONCERN, CHECK FOR LEAKS NONE, ENGINE RUNNING COLD,
SUSPECT THERMOSTAT
REPLACE THERMOSTAT AND RADIATOR CAP. CAP LOOKS OLD, TOP OFF
COOLANT AND BLEED SYSTEM. ROAD TEST. ENGINE STARTED TO COOL
OFF ON ROAD TEST, CONSULT WITH 512. RECHECK FOR AIR IN
SYSTEM, NONE. SUSPECT THAT THE INTAKE MANIFOLD GASKETS
TABS HAVE ROTTED THRU AND LEAKING COOLANT BACK INTO
ENGINE. WILL HAVE TO REMOVE INTAKE MANIFOLD
CUSTOMER DECLINES, SEE ESTIMATE.
Anyone ever heard of such a thing causing low temp?? ... leaking gasket that
isn't dumping coolant outside of engine, nor into crankcase as there is no
coolant in oil or white smoke in exhaust?? Can this be just allowing
coolant flow that is bypassing the thermostat and keeping engine temp very
low??
I'm assuming the dealership really did change the thermostat... "assume" is
a dangerous word... but they billed him 288.03 total!
Ha! Estimate was $85 (I guess to just see if heat is really poor), then
revised to $250.00, then revised again to $299.00 !!!!
Below that is another estimate:
INTAKE MANIFOLD GASKETS: $495.00
PLUS LUBE OIL AND FILTER: $29.95
at $300 to do the thermostat, I'd guess the intake gasket job would get
"revised" a couple times along the way as well???
And experience or thoughts regarding this engine running too cold that can
be something other than thermostat bad???
Thanks!

To check coolant temp vs the guage, I pop the radiator cap off (when
cold of course) and place a thermometer in the coolant.
Start the engine and warm it up, watch the temp and coolant. The coolant
will circulate when the thermo opens, eventually the temp will
stabilize, and should be close to 195 or the thermo temp. If your
scanner reads the same as the dash gauge then both of the temp sensors
are good. Did you drive and Check the temp? The ECM sensor could be bad
above 125F.
Also a rich mixture will cause a temp drop, not sure if it would cause
your problem. But when the temp is high enough the ECM will richen the
mixture to cool things off. Take a look at the Fuel pressure regulator
and see if its leaking, this is common with old FP diaphrams.
Cheers

Yeah thanks, it runs right... block learn...integr... no signs of radical
enrichment, stumble, misfire,...
definitely just not running up to temp... to tell the truth, I'm wondering
if the dealer never even changed the thermostat! I'm a mechanic myself part
time (bad back) and I've seen insane quotes for outragous prices for work
that did NOT need doing whatsoever... like 600 for rear brakes on a Jeep
added on to an estimate for 1200 for exhaust work. I tightened the front
nuts which swung the front pipe back into place to stop hitting the front
driveshaft, the proceeded to the rear brakes (the job I thought I'd make a
decent buck doing) to find it had aftermarket linings in it that weren't
even dirty yet... no wear whatsoever!
Anyway, that's getting off topic, but this rig just acts to me like it needs
a thermostat. Unless there are passages in the intake that are normally
quite restricted by the gasket and now are not due to these (tabs rotted),
and these passages allow much flow through the bypass (which I thought only
really went to the heater core)...
Anyone know what "consult with 512" means?
I've googled that along with searching out "... cold running... and intake
gasket problems..." and find nothing along the lines of an intake gasket
making it run cool, making me think the dealership was pumping him big time.
If problem is intake gasket, that is fine. And I'd probably refresh the
injector fpr unless it was bone dry and looked like it had maybe already
been done. I don't think rich mixture would make it run cool to this
extent.

Martin, when you put a thermometer in the radiator cap hole you are
measuring
the coolant temp on the cold side of the radiator.
On my 97 Yukon with a new dual core radiator, a calibrated industrial
thermometer reads
about 150-160 degrees vs. 193-197degrees on the scanguage even with the
airflow to the
radiator blocked off with a sheet of plastic and the engine running at hi
idle (about 1200 RPM).
The way the heater/bypass lines are routed I would suggest that the OP have
his friend
try to back flush the heater core/hoses to see if that doesn't solve his
problem before he throws
any more money at it. Also have him burp the cooling system to make sure
there is no air trapped
in there. Remember, this is a van so there is more hose to plug up or trap
air.
I always try the cheap/free things before I spend any money.
As Scotty said in Star Trek, "The more they tech the plumbing, the easier it
is to stop up the drain."
I'm thinking this could solve both problems.
Regards
JR

He
F.
seem
35
spelled
"assume"
then
cold
stabilize,
and
have
it
OP here : )
Heat was fine and temp guage fine until recently.
I don't think problem is plugged heater core, and that certainly wouldn't
make engine run cool.
Temp guage 125 while scanner reads 120. Drive down road and both drop
nearly 10 more degrees.
I need to replace his shifter cable later this week (pops off ball on
steering column sometimes) so I'll do his thermostat for him while I have it
here just to be sure. I still find NOTHING regarding what dealership claims
may be the problem!

What kind of climate/temperature are these being recorded in? Cooling
system is pretty simple. If it is running cold like this, unless heater
bypass circuit is taking a lot of heat from water (meaning it is very
cold out) you have a leak in thermostat area that is letting too much
coolant into radiator before engine fully warms up. Try a different
Tstat of a different brand too and make sure that there is not bypass
leakage in housing around it.

I must disagree with that statement, although I have seen bad clutch fans
cause overheating at low speeds and in traffic.
Thermostat should keep it hot enough even if fan was a direct mount, as well
as when the rad is going down the road at 55, which is more air flow than by
the fan alone. But I'll count you in as one more vote against the intake
gasket foolishness stated by the dealership mechanic! And I can tell by the
sound that the fan clutch is working.

Thanks to you and all responses.
I'd have to say the consensus here is what my own thinking is...
This intake gasket thing is total BS!
Either the thermostat was a bad one off the shelf, or it never go changed.
And either the mechanic involved is a total idiot, or making it up as he
goes to try to rake some more bucks out of this poor fellow.
My personal thought is the latter of both those two statements!
I'll follow up when it comes back for me to work on!
In2

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